There is a need for self-contained water-pumping systems that can raise well water to the surface using collected radiant solar energy as a primary energy source so as to be able to function for long periods with little, if any, in the way of external input of supplies, including fuel. Such a pump is desirable in remote or poor areas where electricity or hydrocarbon fuels, for example diesel oil, are expensive or unavailable. To meet the needs of these areas, such a water-pumping system should require little, if any maintenance and, unlike internal combustion engines, have few demands for replacement parts.
A broad objective of the present invention is to provide an improved solar-powered steam-generation system which is particularly applicable for use in the poorer, drier countries of the world, for example, in much of Africa, for tasks including pumping water for drinking and personal use or for irrigation. A further objective is to provide a water-pumping system driven by such a generator which system is economical, self-contained low maintenance and does not require a supply of fuel. It is particularly challenging to provide a system which while being very low maintenance has a low enough capital cost to be affordable. In 1991 U.S. dollars, this capital cost should be of the order of a dollar per gallon per day on a sustainable basis although fifty cents per gallon per day for a capacity of the order of tens of thousand of gallons per day is a more desirable target.
The art is replete with proposals for solar-powered water pumps, most of them overly complex, which are either technically inadequate, typically because they fail to provide effective solar energy collection means and therefore fail to maintain sufficient temperature gradients, or are hopelessly expensive, or both. It is doubtful whether most of the prior art systems can pump worthwhile quantities of water on a continuous basis, and none is believed to do so with adequate economy.
Other possible uses of the raised steam include water-heating, for example for cooking, and electricity generation. However, the efficiency of such applications is questionable with existing technology, and the preferred application is for raising or pumping water as this has already been shown to be practicable in an economical manner.
The present invention is concerned with systems that are commercially feasible for purchase by communities such as villages of several hundreds or thousands of people. This imposes considerable constraints on the technology that can be used. Put simply, such systems must be capable of pumping a lot of water consistently with very low running costs and for a modest capital investment. The capital cost rules out technologies such as focussing reflector arrays and photovoltaic collectors, which have expensive components and usually require tracking means to follow the sun. Furthermore, currently known such systems tend to require expensive maintenance components. They are too "high-tech" to be suitable as the primary energy source for the systems of the present invention, although small-scale structures, such as photovoltaic panels may have application for low-capacity control or subsidiary purposes where a higher potential energy than the steam-generation means provides, is required.
Similarly, running and maintenance costs and skills rule out diesel or other internal combustion engine generators.
Moan U.S. Pat. No. 4,346,694 describes a system in which an array of passive solar-energy collection elements heat air in a plurality of streams that are consolidated in an insulated manifold to provide an open-circuit hot air stream. No use is described or suggested for the low-pressure hot air output of the Moan system. Preferred collector elements are double-walled evacuated glass tubes within which distribution tubes provide for two-way air flow and the Moan system offers good collection efficiency combined with moderate capital and low maintenance costs.
In a disclosure entitled "Solar Powered Water Pump" purportedly filed in the United States Patent and Trademark Office on Apr. 1, 1991 with rights accruing to WorldWater Inc. (hereinafter called "the WorldWater text"), inventor(s) unknown, there is described a water-pumping system broadly designed to meet the foregoing objectives, which system uses solar-generated hot air, produced, for example, with Moan's collector array, to raise steam. In an important disclosure, the WorldWater text uses the head of steam to drive a diaphragm pump for pumping water. Surprisingly good results are obtainable, with good water deliveries in modest solar radiation conditions. The disclosed system is economical and efficient with low maintenance costs.